Magnetic resonance tomographs are imaging devices which, for imaging an examination object, orient nuclear spins of the examination object with a strong external magnetic field and by an alternating magnetic field, excite them to precession about this orientation. The precession or return of the spin from this excited state into a state with lower energy generates an alternating magnetic field as a response, also designated a magnetic resonance signal, which is received via antennas.
With the help of magnetic gradient fields, a position encoding is impressed upon the signals, which subsequently enables an allocation of the received signal to a volume element. The received signal is then evaluated and a three-dimensional imaging representation of the examination object is provided. The representation created gives a spatial density distribution of the spin.
The magnetic resonance signals received are very weak, e.g., in part only just over the noise limit. At the same time, the excitation pulses have energies in the kilowatt range and for the gradient fields, currents of several hundred amperes flow.
Due to the strong fields and also indirectly due to mechanical-electrical interactions, in the region of the patient accessways, electrical potentials may form, and, on their equalization, small discharges may take place which lead to brief broad-band interference pulses, known as spikes. Hereby, during the subsequent image processing, through the Fourier transform, from individual spikes, whole patterns of artifacts distributed over the image may arise.
From German patent publication DE 10 2016 223478, a magnetic resonance tomograph is known which acquires the physiological data of the patient and thereby orients the sequences of image acquisition temporally so that the acquisition of the physiological signals is not disrupted.